The invention relates to a device for voltage stabilization in a motor vehicle. More specifically, the invention relates to a device for stabilizing a motor vehicle electrical system during a starting process, which detects a voltage drop without the need for an external control signal and takes a voltage limiting action without a time delay.
Means for stabilizing a motor vehicle electrical system is known in principle. For a startup in a motor vehicle there is the fundamental problem that the starter of the vehicle requires a high current, which the starter takes from the vehicle battery. The high current draw by the starter leads to a voltage drop at the battery terminals, which results in a voltage drop across the electrical system. All electronic components and equipment of the motor vehicle are thus affected by such a voltage drop. The depth of a voltage drop, which must survive all the components connected to the electrical system and equipment without malfunction and undamaged, is specified by the manufacturers of the respective components. If the battery is weakly charged, damaged, or an old battery, the voltage drop may still be lower than the clamp voltage specified by the manufacturer. Such low voltage drops can cause malfunctions that can damage the on-board network connected components and devices. Therefore, it is necessary to limit a stress on the battery terminals to provide or limit the starter current so that the voltage at the battery terminals cannot fall below a predetermined threshold.
Known methods for stress relief on a battery can be essentially divided into passive and active methods. Passive means for limiting the voltage drop use resistors which are introduced between the battery and the starter to limit the starting current. Such passive methods are particularly easy to implement, but cause high energy losses and are relatively inflexible. Further, passive methods have to be tuned to a specific type of battery, and must therefore be redefined when changing the battery. Active voltage limiting methods typically use a pulse width modulation (PWM), in combination with resistors, semiconductors, and/or other components.
Regardless of the type of voltage drop limiting method, in the prior art, a voltage drop limiting action is initiated only when an on-board network detects the voltage drop. After detecting the voltage drop, the on-board network then sends a corresponding control signal to a device for stabilization of the motor vehicle electrical system, which consequently initiates an appropriate responsive action to limit the voltage. This measure is, for example, at the limit of the starter current and/or the activation of an additional energy source.
A disadvantage of the prior art devices is, thus, that a corrective action is only taken after the detection of a voltage drop in the electrical system, i.e. only in case of failure, and a message is sent to an on-board network and the responsive action is determined. The time period that elapses between detecting a voltage drop in the electrical system and the activating of a responsive voltage drop-limiting action may be sufficient to cause damage to the components and devices due to the voltage drop.
An object of the present invention is therefore to provide a device for stabilizing a motor vehicle electrical system during a starting process, which detects a voltage drop without the need for an external control signal. It is further an object of the present invention to automatically and immediately take an appropriate voltage limiting measure, without a time delay.